Much recent interest has been directed towards the development of packet radio communication systems capable of providing data-intensive communication services. For instance, the IEEE 802.15.3a operating specification contemplates an Orthogonal Frequency Division Multiplexing (OFDM) Ultra Wide Band (UWB) communication system, capable of communicating data over wide bandwidths and short ranges.
Ultra Wideband is defined as any radio technology having a spectrum that occupies a bandwidth greater than 20 percent of the center frequency, or a bandwidth of at least 500 MHz. Modern UWB systems use modulation techniques such as OFDM to occupy these extremely wide bandwidths.
OFDM distributes data over a large number of carriers that are spaced at precise frequencies. This spacing provides the orthogonality in this technique, which prevents interference from adjacent tones. The benefits of OFDM include high-spectral efficiency, resiliency to radio frequency (RF) interference, and lower multipath distortion. OFDM used for UWB transmission results in a novel physical layer system for the enablement of high bit rate, short-range communication networks.
The seminal article on OFDM is “Data Transmission by Frequency-Division Multiplexing Using the Discrete Fourier Transform”, by S. B. Weinstein and Paul M. Ebert in IEEE Transactions on Communication Technology, Vol. com-19, No. 5, October 1971, the contents of which are hereby incorporated by reference.
The Ultra-Wide Broadband (UWB) spectrum from 3.1-10.6 GHz is divided into 14 bands of 528 MHz each, implying 14 carrier frequencies. These bands are further grouped into band groups, each having two or three adjacent frequency bands (see FIG. 1).
The most common method used to generate each band frequency involves using a separate frequency source for each band frequency or a combination of such sources. There are some methods by which a single frequency source can generate several frequencies. However, since these methods require separate components for each frequency generated, the number of components increases while attempting to generate more band frequencies, resulting in a more complicated system.
Current state of the art implementations generate a maximum of seven carrier frequencies and do not completely comply with the current band plan of the Multi-band OFDM Alliance (MBOA) proposal shown in FIG. 1. Very few of the implementations use the concept of frequency switching within a particular band as is specified in the MBOA proposal in the mode of operations. This makes the implementation bulky and power hungry when the number of band frequencies to be generated increases.
Therefore, it would be desirable to have a frequency synthesizer capable of generating all 14 frequencies efficiently, while providing fast hopping capability within the band groups. Apart from this, the frequency synthesizer also should generate the baseband clock which could be 1056 MHz or 528 MHz depending on the baseband requirement. To lower cost, the frequency synthesizer, along with the UWB system, should be able to use components that are currently widely used for existing wireless standards.